(CBS/AP) GOLDEN, Colo. - Austin Sigg, the teenager who prosecutors say confessed to killing 10-year-old Jessica Ridgeway and attacking a runner has been formally charged as an adult in both cases, reports CBS Denver.

Prosecutors filed counts against Sigg, 17, on Tuesday, including murder, robbery and sexual assault on a child.

Sigg didn't speak during the hearing and didn't look at his relatives in the courtroom in Golden.

Eight relatives of Ridgeway also watched proceedings, including her mother. They each wore purple which is Jessica's favorite color.

If convicted, Sigg could face up to 40 years in prison, reports the Denver Post. Because he is under 18, neither the death penalty, nor life in prison without parole are options for Sigg. Sources tell the newspaper that DNA evidence against Sigg is overwhelming.

Ridgeway disappeared while walking to school on Oct. 5. Her body was found on Oct. 10.